OK every kid has tried to walk to dog on the bike, and most likely failed miserably. I stumbled on this article for leashes for bikes for dogs. They look interesting but I still see one problem, the dog suddenly seeing a squirrel and going sideways to you (and you go DOWN).
http://www.amazon.com/gp/offer-listing/B00J4YAJU4/ref=dp_olp_0?ie=UTF8&condition=all — $80
http://www.thedogoutdoors.com/walkydog-dog-bike-leash.html — $50, looks promising
http://www.thedogoutdoors.com/dog-bike-leash.html – $150, looks pretty stable, but….costly
http://www.runningk9.com/items/springer-dog-exerciser/springerblack-detail.htm – I like this one, but at $130 a whack….